Electric power plants generate electricity using various types of power generators, which may be categorized, depending on the energy used to generate electricity, into thermal, nuclear, wind, hydroelectric, etc., generators. Each of these various types of generators operates under different sets of constraints. For example, an output of a thermal generator is a function of the amount of heat generated in a boiler, wherein the amount of heat is determined by the amount of fuel that can be burned per hour, etc. Additionally, the output of the thermal generator may also be dependent upon the heat transfer efficiency of the boiler used to burn the fuel. Similar types of constraints exist with other types of electric power plants. Moreover, for most power plants using boilers, the desired steam temperature set-points at final superheater and reheater outlets are constant and it is necessary to maintain steam temperature close to the set-points within a narrow range at all load levels.
Fuel burning electric power generators operate by burning fuel to generate steam from water traveling through a number of pipes and tubes in the boiler. The steam is used to generate electricity in one or more turbines. However, burning of certain types of fuel, such as coal, oil, waste material, etc., also generates a substantial amount of soot, slag, ash and other deposits (“soot”) on various surfaces in the boilers, including the inner walls of the boiler as well as on the exterior walls of the tubes carrying the water through the boiler. The soot deposited in the boiler has various deleterious effects on the rate of heat transfer from the boiler to the water and thus on the efficiency of power generators using the boilers. Therefore, it is necessary to address the problem of soot in fuel burning power plants that burn coal, oil, and other such fuels that generate soot. It should be noted that while not all fuel burning power plants generate soot, for the remainder of this patent the term “fuel burning power plants” is used to refer to those power plants that generate soot.
Various solutions are used to address the problems caused by generation and presence of soot deposits in boilers of fuel burning power plants. For example, fuel burning power plants use soot removing devices or equipment known as soot blowers as part of operating boilers. Fuel burning power plants use various types of soot blowers to spray cleaning materials through nozzles, which are located on the gas side of the boiler walls and/or on other heat exchange surfaces. Such soot blowers use any of the various media such as saturated steam, superheated steam, compressed air, water, etc., for removing soot from the boilers.
However, soot blowing activity affects many aspects of boiler operations. For example, soot blowing affects heat transfer efficiency, steam temperature control, levels of NOX inside the boilers, etc. For example, soot blowing in a water wall section of a boiler increases heat absorption rate in the water wall section, which reduces the temperature of the flue gas leaving the furnace section of the boiler. As a result, the flue gases entering the convection section may have a lower temperature, resulting in lower heat absorption in a superheat section and a reheat section of the boiler, and therefore, reducing the steam temperature in these sections as well. On the other hand, soot blowing in the convection section of a boiler increases the heat absorption rate, resulting in increased steam temperature.
Various qualitative effects of soot blowing are well known. However, it is difficult to determine precise quantitative impact of soot blowing on the efficiency and steam temperature of fuel burning power plants. Compensation techniques used by existing control systems include using a feedback PID controller that modulates at least one of spray flow levels, burner tilts, and flue gas bypass dampers, to compensate for the effect of soot blowing. However, often such feedback compensation action is reactionary and it may cause significant steam temperature swings. Therefore, it is necessary to develop a systematic method of constructing a feed-forward signal to compensate for the impacts of soot blowing.
In today's competitive electrical utility industry where utilities use various sophisticated control systems to manage operating costs and increase efficiency of power generators, it is important to understand the effects of operating soot blowers so that operators and control systems may make informed decisions about how to compensate for the disturbances caused by soot blowing. Thus, there is a need to provide better quantitative information about the impact of soot blowing so that any adverse or negative impact of soot blowing can be compensated for more effectively.